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Abstract:

In a method for diagnosing a valve in a fluid supply line to a suction
line of an air system of a combustion engine, the fluid supply line being
is part of an exhaust-gas recirculation system or a crankcase ventilation
system, when the valve is actuated, a first pressure in the suction line
is monitored for change, and an error of the valve is detected if the
change of the first pressure lies outside a specific reference range when
the valve is actuated.

Claims:

1. A method for diagnosing a valve in a fluid supply line to a suction
line of an air system of a combustion engine, wherein the fluid supply
line is part of an exhaust-gas recirculation system or a crankcase
ventilation system, the method comprising: monitoring a first pressure in
the suction line for a change when the valve is actuated; and detecting
an error of the valve if the change in the first pressure during the
actuation of the valve lies outside a specified reference range.

2. The method as recited in claim 1, wherein a magnitude of the actuation
of the valve is taken into account in the diagnosis.

3. The method as recited in claim 2, wherein the reference range is
specified on the basis of operating characteristic values of the air
system.

4. The method as recited in claim 3, wherein at least one of a
temperature of the air system, a position of a throttle valve of the
suction line, a camshaft position of the combustion engine, an engine
speed of the combustion engine, and a position of another valve of the
air system is considered in specifying the reference range.

5. The method as recited in claim 4, wherein a pressure differential
between the first pressure in the suction line downstream from the valve
and a second pressure in the fluid supply line upstream from the valve is
considered in specifying the reference range.

6. The method as recited in claim 1, wherein the reference range is a
predefined reference range.

7. The method as recited in claim 5, wherein the error is detected only
if the air system satisfies at least one predefined condition.

8. The method as recited in claim 7, wherein the error is detected only
if the air system is in one of a steady-state or a quasi-steady state at
an instant prior to the actuation of the valve.

9. The method as recited in claim 8, wherein the one of the steady-state
or the quasi steady state is detected if at least one of a rotational
speed of the combustion engine is essentially constant, the position of
the throttle valve in the suction line is essentially unchanged, the
position of another valve in the air system is essentially unchanged, and
the pressure in the suction line is essentially constant.

10. The method as recited in claim 7, wherein the error is detected only
if the pressure differential between the first pressure in the suction
line and the second pressure in the fluid supply line upstream from the
valve lies above a specified threshold value one of prior to or during
the actuation of the valve.

11. The method as recited in claim 10, wherein the first pressure in the
suction line is an intake manifold pressure determined by one of an
intake manifold pressure sensor or a differential-pressure sensor.

12. A non-transitory computer-readable data storage medium storing a
computer program having program codes which, when executed on a computer,
performs a method for diagnosing a valve in a fluid supply line to a
suction line of an air system of a combustion engine, wherein the fluid
supply line is part of an exhaust-gas recirculation system or a crankcase
ventilation system, the method comprising: monitoring a first pressure in
the suction line for a change when the valve is actuated; and detecting
an error of the valve if the change in the first pressure during the
actuation of the valve lies outside a specified reference range.

13. An electronic control unit for diagnosing a valve in a fluid supply
line to a suction line of an air system of a combustion engine, wherein
the fluid supply line is part of an exhaust-gas recirculation system or a
crankcase ventilation system, comprising: means for monitoring a first
pressure in the suction line for a change when the valve is actuated; and
means for detecting an error of the valve if the change in the first
pressure during the actuation of the valve lies outside a specified
reference range.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for diagnosing a valve of
a fluid supply line, and to a computer program set up for this purpose.

[0003] 2. Description of the Related Art

[0004] Different fluids may be provided in the fresh-air suction line of
an internal combustion engine. For example, the crankcase in an internal
combustion engine is able to be ventilated, and this ventilation can be
rerouted to the fresh-air suction line of the engine (in particular into
an induction manifold of the combustion engine). In addition, exhaust-gas
recirculation lines are known, via which combustion gases are returned to
the suction line of the combustion engine.

[0005] Such supply lines are able to be monitored with the aid of
diagnoses. For example, published German patent application document DE
10 2008 041 804 A1 describes the diagnosis of an exhaust-gas
recirculation system. The idea of this method is to use a pressure ratio
within the air supply section (that is to say, the pressure upstream from
the throttle valve versus the pressure downstream from the throttle
valve) or between the air supply section and the exhaust-gas section
(i.e., the intake manifold pressure versus the exhaust-gas recirculation
pressure) or via a position of a throttle valve of the intake manifold in
order to determine whether an adverse effect (especially sooting) is
manifesting itself in the exhaust-gas recirculation system. To do so, the
mentioned values of the pressure differential are compared to a reference
value.

[0006] Published German patent application document 10 2008 002 721 A1
discloses the diagnosis of a ventilation system; in this case an error of
the ventilation system can be detected through a brief interruption of
the ventilation line between the crankcase and the air system of the
combustion engine, and by monitoring the Lambda value of the exhaust gas
of the combustion engine.

[0007] Published German patent application document DE 10 2009 002 746 A1
proceeds from a method for checking the operativeness of a tank
ventilation system of a motor vehicle which is equipped with an internal
combustion engine providing charge detection, based on the intake
manifold pressure. The tank ventilation valve is opened in defined manner
and/or actuated in closing manner, and the operativeness of the tank
ventilation valve is inferred from the intake manifold pressure that
comes about in the process.

BRIEF SUMMARY OF THE INVENTION

[0008] In accordance with the present invention, a simple diagnosis of the
appropriate valve is able to detect a large number of the errors in such
systems in a reliable and uncomplicated manner even in an exhaust-gas
recirculation and crankcase ventilation, in that a pressure in the air
system of a combustion engine is monitored for change during an actuation
of the valve. In the method according to the present invention, a
diagnosis of a valve of a fluid supply line of an exhaust-gas
recirculation line or of a crankcase ventilation, to a suction line of an
air system of a combustion engine takes place. In the process, a first
pressure in the suction line is monitored for change when the valve is
actuated, and an error of the valve is detected if the change of the
first pressure lies outside a specific reference range during the
actuation of the valve. The reference range is a pressure value range
within which the pressure change caused by the valve actuation is
expected if the valve is operating properly.

[0009] Thus, the diagnosis pertains to controlled valves of a fluid line
in which a pressure sensor is post-connected in the flow direction of the
fluid, in order to determine the pressure in the suction line into which
the fluid line discharges. Via the valve, a mass flow of the fluid is
routed into the suction line of the air system, especially into an intake
manifold. In the steady state, the discharging mass flow corresponds to
the inflowing mass flow. As the discharging mass flow from the intake
manifold increases, the pressure in the manifold rises, with otherwise
unchanged operating conditions. When the valve of the valve supply line
is opened, the intake manifold pressure therefore rises. When the valve
is closed, the intake manifold pressure drops correspondingly. This is
able to be checked by thresholds (or by reference ranges defined with the
aid of these thresholds), e.g., by a threshold for the delta of the
pressure in the intake manifold prior to the change in the valve
position, and some period of time following the change in the valve
position. Different thresholds make it possible to check the change in
the valve position both in terms of quality and quantity. Errors, such
as: the valve does not open at all/sticks, the valve opens less than
expected, the valve has soot deposits, the valve opens to a greater
extent than expected, the valve does not close at all, are able to be
detected in this manner.

[0010] The diagnosis is made possible by a measured pressure in the flow
direction of the valve. If the valve is opened or closed, then this
affects the pressure, and this effect is able to be checked by a measured
pressure or by a determined change in pressure. In the case of a
crankcase ventilation, just like in the case of an exhaust-gas
recirculation, the flow direction is into the suction line or into the
intake manifold. Nowadays, an intake-manifold pressure sensor or a
differential-pressure sensor is frequently already installed in the
intake manifold. No additional components are therefore required to
perform the described diagnosis.

[0011] The selectivity of the diagnosis is a function of the operating
point, that is to say, the additional quantities of the air system or the
conditions therein. In the first order, it depends on the ratio of the
mass flow flowing via the valve, and the discharging mass flow from the
intake manifold. In order to improve the selectivity even further,
additional influences on the intake-manifold pressure, such as the engine
speed, temperature, camshaft position, and the position of other valves
may be taken into account. Toward this end, for example, it may be
checked that these influences vary only to a predefined degree during the
diagnosis, so that a usable diagnosis result is obtained. It is also
possible to compensate for these influences, for instance by converting
the change in the influences into a pressure change and then to consider
this in the evaluated pressure delta or in the reference ranges utilized
for the comparison. In so doing, for instance, it is also possible to
compensate for the pressure differential of the pressures upstream and
downstream from the valve. The monitored pressure delta in the intake
manifold varies linearly with the pressure upstream from the valve and is
superimposed to the pressure ratio in non-linear fashion. The linear
change is able to be compensated very well.

[0012] Up to a pressure ratio of approximately 0.54, the non-linear change
has no effect; after that, the influence becomes increasingly stronger up
to a vertical gradient at a pressure ratio of 1 (flow velocity across
throttle according to Saint-Venant and Wantzel). This may be taken into
account by a pressure delta as a switch-on condition or via the pressure
ratio. The flow velocity is able to be compensated as well and the
diagnosis range thus expanded as a result.

[0013] In one development the reference range therefore is able to be
calculated on the basis of variables of the air system. Toward this end,
algorithms or characteristic maps may be stored in a control unit and
then be used to calculate an expected pressure change from currently
measured or likewise calculated variables of the air system as a function
of the magnitude of the actuation of the valve, and to furthermore
calculate the reference range utilized for the comparison with the
determined pressure change on this basis. This produces an especially
flexible system that allows a diagnosis even under complex conditions,
for instance when changes occur in different variables of the air system.

[0014] For example, the following may be entered in such a calculation of
the reference range: a temperature of the air system, a position of an
actuator of the air system, especially a throttle valve of the suction
line, a camshaft position of the combustion engine, an engine speed of
the combustion engine and a position of another valve of the air system.
These quantities have been found to be especially important quantities of
the air system, whose variations could influence the calculation to a
considerable degree.

[0015] To be taken into account as another important quantity for such a
calculation of the reference is a pressure differential between the first
pressure in the suction line downstream from the valve, and a second
pressure in the fluid supply line upstream from the valve. A prerequisite
in this context is a determination of the second pressure with the aid of
a pressure sensor or on the basis of a calculation using other available
quantities.

[0016] As an alternative to the reference range calculation, a diagnosis
is possible also on the basis of a comparison with a predefined reference
range. This method is particularly easy to carry out. In so doing, the
reference range may also be one of several predefined reference ranges,
so that a flexible error detection furthermore is possible within the
framework of the predefined reference ranges.

[0017] In the case of a comparison of the pressure change with a
predefined reference range and also a comparison with a calculated
reference range, it is advantageous to perform the diagnosis only under
certain conditions of the air system and furthermore, to detect an error
only under certain conditions of the air system. The reason for this is
that an error detection is especially difficult or may include errors in
certain conditions of the air system. In other words, such a marginal
condition increases the quality of the detected errors considerably.

[0018] It is particularly advantageous if the error is detected only if
the air system is in a steady-state or quasi-steady state, that is to
say, if no or no large changes in quantities of the air system are at
hand just then, especially changes in the pressure in the suction line or
in the intake manifold. Such a state allows a particularly reliable
diagnosis.

[0019] A steady-state or quasi-steady state of this type is detectable
when a rotational speed of the combustion engine is essentially constant,
when a position of an actuator in the air system, especially a throttle
valve in the suction line, is essentially unchanged, when a position of
another valve in the air system is essentially unchanged, or when several
or all of the conditions apply.

[0020] Another, especially advantageous improvement of the diagnosis
quality is achievable if an error is detected only if a pressure
differential between the first pressure in the suction line and a second
pressure in the fluid intake line upstream from the valve lies above a
threshold value prior to or during the valve actuation. For if the
pressure upstream and downstream from the valve is of equal magnitude or
differs only slightly, no pressure change occurs in the actuation of the
valve. If this additional condition were not provided, the diagnosis
would detect errors.

[0021] In one preferred development, all steps of the described method are
controlled by a computer program which is stored on an electronic storage
medium in an electronic control unit, in particular an engine control
unit.

[0022] It is understood that the features mentioned above and still to be
explained below may be used not only in the indicated combinations, but
in other combinations as well, or by themselves, without departing from
the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 schematically shows a section of a combustion engine.

[0024] FIG. 2 shows the steps of a method for performing a valve
diagnosis.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention is represented schematically in the drawing
with the aid of specific embodiments, and described in detail below with
reference to the drawing.

[0026] The cylinders of a combustion engine are supplied with air via an
air system. The air is admitted into the appropriate cylinder with the
aid of an intake valve. FIG. 1 schematically shows intake manifold 1 and
throttle valve 2 as components of such an air system. The air charge
supplied to the cylinders via intake manifold 1 is able to be influenced
by the position of throttle valve 2. Upstream from the throttle valve
(indicated by arrow 3) is an air supply line. Downstream from the
throttle valve (indicated by arrow 4) are the intake valve and cylinder
of the combustion engine. Furthermore, a pressure sensor 5, which
measures the pressure in intake manifold 5, is situated on intake
manifold 1, downstream from throttle valve 2. In addition, a fluid supply
line 6 discharges into the intake manifold downstream from the throttle
valve. A valve 7 is situated inside fluid supply line 6 in order to
control the supplied fluid quantity. The supplied fluid comes from a
fluid source upstream from valve 7 (indicated by arrow 8).

[0027] When the combustion engine is operated, the pressure in a crankcase
increases, e.g., by collecting combustion gases from the combustion
chambers and by the formation of oil mist. For one, this may have a
detrimental effect on the operation of the cylinders and, for another, it
could also lead to a leakage of hydrocarbons and oil mist into the
environment of the combustion engine. To avoid the generation of
increased pressure in the crankcase, crankcase ventilation is provided,
of which a ventilation line is part. In one preferred development of FIG.
1, fluid supply line 6 is such a ventilation line of a crankcase
ventilation.

[0028] In combustion engines having exhaust-gas recirculation (AGR),
combustion gas from the cylinders is discharged via an exhaust-gas
section. An AGR line is provided between this exhaust-gas section and an
intake manifold of the combustion engine. In one alternative development
of FIG. 1, fluid supply line 6 is such an AGR line. As a result, valve 7
is an AGR valve, via which an AGR rate is able to be adjusted.

[0029] FIG. 2 schematically shows an exemplary sequence of a diagnosis of
a valve of a fluid line, as it is shown in FIG. 1 by way of example. In a
first step 21, it is determined whether the valve is actuated. If no
actuation is detected, branching to step 22 takes place and no diagnosis
is performed. The actuation discovered in step 21 may be an actuation
specifically provided for diagnostic purposes, but it could also be an
actuation provided during normal operation of the combustion engine. If
an actuation of the valve has occurred, branching to step 23 takes place.
The intensity of the actuation (i.e., the requested valve opening or
closing) may likewise be taken into consideration in the method. This
allows a diagnosis to be dispensed with if the actuation is minimal. An
expected change in pressure may also depend on the magnitude of the valve
opening or the valve closing.

[0030] In step 23 it is determined whether the conditions in the air
system are suitable for performing a meaningful or reliable diagnosis. To
do so, for example, it may be checked whether the pressure in the air
system, more precisely, in the suction line or the intake manifold, is
essentially constant immediately prior to the actuation or within a
specified time interval prior to the actuation. Furthermore, it may also
be checked whether a throttle valve position is essentially unchanged in
a period prior to the actuation, whether an engine speed is essentially
constant, whether other valves in the air system have essentially
unchanged positions, etc. If the prescribed conditions are not met,
branching to step 24 takes place and the diagnosis will not be performed.
If the prescribed conditions are satisfied, branching to step 25 is
implemented.

[0031] In step 25 it is checked whether a pressure differential between
the pressure upstream from the valve to be checked and the pressure
downstream from the valve to be checked is of a magnitude such that a
pressure change is ensured downstream from the valve that is sufficient
for the intended diagnosis when the valve is opened. This step is omitted
if no means are available to determine the pressure on the side of the
valve facing away from the suction line, or if a sufficient pressure
differential is ensured by the system design or is present with a high
degree of probability. As a result, step 25 is optional. If it is
performed and if the pressure differential is insufficient, branching to
step 26 takes place and the diagnosis will not be performed. If the
differential is sufficient or if it is not checked, branching to step 27
occurs.

[0032] In step 27, a pressure change in the suction line is determined.
For example, a gradient or a temporal change or a derivation of a
determined pressure value may be calculated for this purpose. Pressure
values determined by a pressure sensor in the intake manifold at an
instant immediately prior to the actuation of the valve, during the
actuation of the valve, and following the actuation of the valve are
preferably utilized for this purpose. It is also possible to form the
pressure difference between a particular instant prior to the actuation
and a specific instant following the actuation. This value is compared to
a value range to be expected in the corresponding actuation under the
given conditions of the air system. This reference range may either be
selected from a series of predefined reference ranges, or calculated from
quantities of the air system. For example, an actuator position, e.g., a
throttle valve position, a temperature value of the air system, the
engine speed of the combustion engine, the pressure differential upstream
and downstream from the valve, the magnitude of the actuation of the
valve, a camshaft position etc. may be considered in such a selection or
calculation.

[0033] If the pressure change lies within the reference range, that is to
say, the pressure change is within the expected thresholds, branching to
step 28 takes place and the diagnosis is terminated without error output.
If the pressure change lies outside the predefined pressure threshold
values (i.e., outside the reference range), branching to step 29 occurs.
The diagnosis detects an error. This error may be forwarded directly or
be forwarded if a certain number of such errors has been detected.

[0034] The described method may also be repeated continuously, either
until an error report or possibly also a positive acknowledgment has been
received. Once the report has been transmitted, the diagnosis may pause
or be continued immediately, or start from the beginning again.

Patent applications by Matthias Heinkele, Leonberg DE

Patent applications by Michael Drung, Muehlacker DE

Patent applications by Robert Bosch GMBH

Patent applications in class Exhaust gas recirculation system (EGR)

Patent applications in all subclasses Exhaust gas recirculation system (EGR)